Outer interface

The driving force for migration is established by the different electrochemical potentials (AU) that exist at the two interfaces of the oxide. In other words, the electrochemical potential at the outer interface is controlled by the dominant redox species present in the electrolyte (e.g. O2). 

From this definition it follows that at the outer interface pj of the innermost slice s = 1, and at the inner interface pg i of the outermost slice s = S, the immittance matrix takes the values... 

Model catalysts have to be prepared directly on the IRE, which can be a challenging task. Thin metal films are an important type of model catalyst and can be made, for example, by physical vapor deposition or sputtering of the metal onto the IRE. Most suitable IRE materials for such applications are Ge and Si. The former has a high refractive index of 4.0, which results in a small penetration depth and therefore good discrimination against bulk solvent. The metal film should not be too thick, so that the evanescent field can reach the outer interface of the metal film. 

Solution. The outer interface is concave and the inner interface is convex with respect to the 0 phase. The concentrations of B maintained in equilibrium in the a phase at the outer interface, c (ft, and at the inner interface, c f, are given by Eq. 15.4. The concentration difference across the shell is therefore... 

The flux is therefore directed toward the outer interface, causing the spherical shell to shrink toward its center under the driving force supplied by the decrease in interfacial energy that occurs as a result of the shrinkage. (Note that ultimately the shell will shrink to form a solid sphere of a phase at the origin.)... 

The membrane system considered here is composed of two aqueous solutions wd and w2, separated by a liquid membrane M, and it involves two aqueous solution/ membrane interfaces WifM (outer interface) and M/w2 (inner interface). If the different ohmic drops (and the potentials caused by mass transfers within w1 M, and w2) can be neglected, the membrane potential, EM, defined as the potential difference between wd and w2, is caused by ion transfers taking place at both L/L interfaces. The current associated with the ion transfer across the L/L interfaces is governed by the same mass transport limitations as redox processes on a metal electrode/solution interface. Provided that the ion transport is fast, it can be considered that it is governed by the same diffusion equations, and the electrochemical methodology can be transposed en bloc [18, 24]. With respect to the experimental cell used for electrochemical studies with these systems, it is necessary to consider three sources of resistance, i.e., both the two aqueous and the nonaqueous solutions, with both ITIES sandwiched between them. Therefore, a potentiostat with two reference electrodes is usually used. 

If coupled to the transfer of the target cation, through the outer interface, the anion of the supporting electrolyte of w2 is transferred through the inner one Eqs. (2.84) and (2.85) are still valid for changing X for X, ... 

In Fig. 5.19, the cyclic voltammogram versus the membrane potential M (given in Eq. (2.79)) obtained for a system with two polarizable interfaces (solid line) is presented. The i//cv curve has been also plotted versus the outer interface oul (dashed line) and the inner interface potential ilm (dotted line) with out and inn given by... 

It can be seen that in the central part of the cyclic sweep, the outer potential, out, follows the same trend as the applied potential, E, so in this zone the outer interface presents a behavior similar to that of a system with a single polarizable interface. Concerning the inner interface, "ml is quite sensitive to the external polarization at both extremes of the cyclic sweep, becoming independent of the potential in the central zone of the same. In the inset, it can be seen how the potential pulses are distributed unequally between both outer and inner interfaces [38],... 

Scheme 7.5 Potential-time waveform of SWV obtained from Eq. (7.5) ( , red line), and its distribution between the outer interface ( °ul, dark blue line) and the inner interface ( "", green line). The three index potentials (the outer index potential, out,mdex, the inner index potential, """ index, and the membrane index potential, mdex) are also included (blue line, dark green line, and black line, respectively). Inset figure Distribution of the applied potential red line), between the outer and the inner interfaces (dark blue line and green line, respectively). jnitiai = —450mV,...

In more sophisticated models, it can be considered that both the singlet-oxygen generation and/or the interaction with the quencher can take place also at the interfaces. In vesicles (and membranes), this includes the inner and outer interfaces, which can present different characteristics. 

Nano-inspection of Dielectric and Polarization Properties at Inner and Outer Interfaces in pzt Thin Films... 

These results suggest, that also the top pzt surface has different properties compared to the bulk values. In fact, various theoretical models already suggested the existence of a pure dielectric surface layer [38] to be present on pzt thin films. Here, for the first time, we have given experimental evidence that this is true for both the inner and outer interfaces in pzt on the nanometer scale... 

In conclusion, we reported the investigation of inner and outer interfaces in pzt in order to quantity both the amount of effective ferroelectric polarization and change in dielectric properties. With pfm and kpfm we find a transition layer occurring at the Pt/PZT interface within... 

In all the systems considered above the photosensitizer was embedded in the membrane symmetrically, i.e. identical S molecules are located near both the inner and the outer surfaces of the vesicle membranes. Of great interest would also be to create asymmetric membranes providing a specially organized gradient of the redox potential across the lipid bilayer. Asymmetry of a membrane can be realized, e.g. if one locates the molecules with different redox potentials within the membrane near its inner and outer interfaces. An asymmetric membrane containing the components required for photochemical separation of charges at the lipid // water... 

Note that asymmetry between the inner and outer interfaces was observed also for large unilamellar vesicles [146]. However, the ratios of the rates of 3Chl quenching and the yields of radical-ion products on the inner and outer membrane surface for large unilamellar vesicles are of the opposite character compared with small unilamellar vesicles. 

Basically, the impedance behavior of a porous electrode cannot be described by using only one RC circuit, corresponding to a single time constant RC. In fact, a porous electrode can be described as a succession of series/parallel RC components, when starting from the outer interface in contact with the bulk electrolyte solution, toward the inner distribution of pore channels and pore surfaces [4], This series of RC components leads to different time constant RC that can be seen as the electrical response of the double layer charging in the depth of the electrode. Armed with this evidence, De Levie [27] proposed in 1963 a (simplified) schematic model of a porous electrode (Figure 1.24a) and its related equivalent circuit deduced from the model (Figure 1.24b). 

P.7.a.2. Spatially varying dielectric response in a finite layer, asymmetric, e(z) discontinuous at inner and outer interfaces, no retardation... 

To derive Pb(Z/2) at the interface between the right-hand-side variable layer of thickness Dr and the medium m, begin as before with Eq. (L3.139a) at the outer interface of variable region with half-space R ... 

Fig. 17A (see color insert) shows a ribbon model of the rhodopsin structure indicating the residues assigned to the interface in each helix by a sphere centered on the corresponding of-carbon. Also shown is a sphere on the a-carbon of residue 314, which is located in the interface (see Section III,F). Clearly, these residues define a unique plane of intersection of the molecule with the membrane-aqueous interface. The shaded band in Fig. 17 represents a phospholipid bilayer with a phosphate-phosphate distance of 40 A, the expected thickness of the bilayer in the disk membrane (Saiz and Klein, 2001). The outer interface of the bilayer is positioned so that the polar head groups coincide with the intersection plane defined by the data in Fig. 16. This procedure then fixes the intersection plane of the molecule on the extracellular surface as well.

Katz and Scott [42] solved this problem by the use of low dispersion serpentine tubing as the interface between the exit from the UV detector of the liquid chromatograph and the spectrometer. A diagram of their interface is shown in figure 43. The principle of low dispersion tubing has already been discussed and it is sufficient to say that the outer interface tube was 49 cm long, 0.25 cm I.D. and merely protected the serpentine tube contained inside. The inner serpentine tube had a peak-to-peak amplitude of 1 mm. An example of the chromatograms obtained from a blood sample monitored by both a UV... 

Generally, the membrane potential is completed by three factors the two potential differences at both inner and outer interfaces and a liquid-junction potential that can be formed across the membrane (especially in liquid membranes). Nevertheless, a galvanic halfcell, represented by a membrane electrode immersed in the sample test solution, usually consists of an... 

Figure 3. Scheme of the PL quenching model (A) and and the comparison (B) of experimental quenching rate A, constants (left axis) with calculated probability density functions i/(r) of a Is electron at the outer interface. 

Reference [42] also reported on the hydrophilic polymer PNIPAM which is adsorbed at the outer interface of o/w-droplet microemulsions. Here, the fluctuations are increased... 

As usual, we start the calculation from the small-load approximation. Equation 68 still applies, but the coefficient of reflection at the outer interface of the film now is not imity but (Zf - Z]jq)/(Zf + Ziiq) instead. The amplitude Uf is given by ... 

AT as well as an overtone-dependent Sauerbrey mass. In the absence of such effects, one may conclude that the outer interface of the film is sharp. 

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